This invention relates to blow moulding, and in particular it relates to a new and improved method and apparatus for heating and blow moulding cold parisons to form containers such as bottles and the like.
Numerous products such as foods, liquid soaps, etc. are now packaged and sold in non-breakable containers, referred to generally as "plastic bottles". These containers, which are commonly made from a polyolefin such as polypropylene are normally manufactured, inter alia, by extruding the material into an elongated endless hollow tube. Cut pieces of the tube, referred to as parisons, are used to form the said plastic bottles by blow moulding techniques. Although numerous different materials may be used, for convenience, this specification will refer specifically to polypropylene.
Since the parisons must be hot when they are formed into bottles, the original technique was to take the parisons, as soon as they were formed by the extrusion apparatus, and while they were still hot, and to transfer them directly to the blow moulding apparatus whereat they were stretched and moulded into the desired shape. However, it has been found undesirable to necessarily link together the process of forming the parisons and the process of forming bottles from the parisons. To the contrary, it has been found more desirable to separate these two functions. The parisons can then be formed into bottles at a latter time or they can be sold to others who may have facilities for forming bottles from parisons but who may not have facilities for initially forming the polypropylene parisons.
The separation of these two functions of course means that the process of forming the bottles must start with cold parisons which must first be heated. Consequently, this technique has become known as the cold parison technique.
In known cold parison techniques, the parisons are first conveyed through an oven with the tubular parisons upright on vertical pins. At a moulding station, a gripper grips the bottom of a given parison and lifts the same upwardly until the top is engaged by a head platen platten which holds the parison and forms the threads and the neck of the bottle at the top thereof as the gripper moves downwardly to stretch the parison, after which the mould is closed and air is blown into the mould from above through the head platten to form the bottle. The mould is then opened and the finished bottle is ejected from the moulding station.
While this known technique has proved relatively successful, it suffers from at least the following disadvantages. First, the apparatus for carrying out this technique is quite complicated. Secondly, the operation of this technique requires a rahter high cycle time of 12 seconds per bottle in mass production (for a given moulding station).
Thus, there exists a need for an improved blow moulding method and apparatus which is more simplified than apparatus known heretofore, and which will permit more rapid, and hence more efficient production of bottles from cold parisons.